New research has revealed a chemical signature of the disease in the blood of those with ME. Scientists from the University of California claim it is similar to a state found in nematode worms called dauer, where the metabolism adjusts to a difficult environment by slowing down.

This hibernation state enables existence, but not much more.

Writing in the journal Proceedings of the National Academy of Sciences, the researchers said that dauer "permits survival and persistence under conditions of environmental stress, but at the cost of severely curtailed function and quality of life."

The aim of the study was to find a simple method of diagnosing ME. There is currently no blood test so doctors must judge whether a patient's lifestyle and behaviour fit the criteria.

Scientists monitored 85 people's blood plasma for metabolites - by-products of the chemical reactions in cells, including the breakdown of molecules to release energy - and more than half of those screened had been diagnosed with ME.

Robert Naviaux, from the University of California, San Diego, found 20 markers of the disease which matched those expected in invertebrates in the dauer state.

This correlation suggests ME could be a response to the environment, making the body mistakenly enter a state designed for adaptation in extreme conditions, the study said.